1. Field of the Invention
The present invention relates to the correction of unbalance of rotation of a rotor of a fan.
2. Description of the Related Art
Currently, electronic devices are equipped with cooling fans for dissipating heat generated inside the electronic devices. The recent enhancement in performance of electronic devices has lead to an ever-increasing amount of internal heat generation, which inevitably calls for improvement of cooling characteristics of the fans. In order to improve cooling characteristics of the fans, air volume and static pressure of the fans need to be increased. For increasing the air volume and static pressure, the fans need to be run at higher speeds. Meanwhile, many electronic devices are used in homes and offices nowadays; for this reason, quiet operation of electronic devices is also demanded.
Noise during operation is caused mainly by an airflow generated by rotation of blades of the fan and making blade passing tones, and vibration associated with the rotation of the fan. As for the blade passing tones, the noise level can be reduced by optimization of the shape of the blades. There is, however, a limit to the reduction of this kind of noise, since the blade passing tones are naturally produced wherever an airflow is generated. On the other hand, the vibration can be reduced to a least possible degree by physically eliminating unbalance of rotation of a rotor.
The vibration value increases as the rotational speed of the fan increases. Since an impeller of the fan is a rotor, physically unbalanced rotation may be caused with respect to the rotation axis. In other words, eccentricity of center of gravity occurs with respect to the rotation axis. While zero is ideal for a value indicating the degree of unbalanced rotation (hereinafter, referred to an unbalanced amount), it is almost physically impossible. Therefore, there arises a need to provide correction of unbalance of rotation so as to bring the unbalance amount of the impeller with respect to the rotation axis, which is produced when the impeller is rotating, as close to zero as possible.
The vibration of the fan not only resonates with the housing of the electronic device and generates noises, but also may adversely affect other electronic components. This is a reason why the vibration of the fan needs to be reduced. And beside, the housing of the recent electronic device have become small in size, hence the installation space for the fan is restricted in the housing. It is required that a space be provided in the air intake area of the fan so as not to hinder entering of air, in order to maximize cooling performance of the fan.